Field of the Invention
This invention relates in general to measuring devices for flowing media, in particular to a new and useful method for determining measurable variable flowing media and for an apparatus for doing this.
The invention relates to blind measuring and detection and in particular to a method for determining a measurable variable of a flowing medium, in particular the flow velocity and/or the material properties, in which the temperature variation of a heated sensor is evaluated in an electronic measuring circuit for the determination of the variable.
From DE-OS No. 29 33 116 a device for measuring the breathing air flow is known where to sensors lying one behind the other at a distance are used, which are heated to constant temperature by a control circuit, the heating energy required therefore representing the measured variable.
Another known measuring device for determining the thermal conductivity of a gas mixture, which is described in German patent DE-PS No. 25 05 669, English patent No. 1544,818 permits the determination of the flow velocity and of the gas composition. For this purpose a resistance sensor is heated by electric current to a certain temperature, which is maintained by an appropriate control circuit. The current occurring in the sensor for the maintenance of the constant temperature constitutes the measured variable. The gas conduction in a flow channel is intermittent, with flow intervals and flowless intervals alternating at equal distances. In the flow interval, the measured variable constitutes a measure of the thermal conductivity and of the flow velocity of the medium. In the flowless interval, the thermal conductivity of the medium, e.g. of a gas mixture, is determined.